1. Field of the Invention
The present invention relates to an apparatus and method for measuring components in bio-tissue. More particularly, the present invention relates to an apparatus and method for measuring blood components such as blood sugar.
2. Description of the Related Art
A human body consists of 73% water and 27% other components. One-third of the water is extracellular, and two-thirds of the water is intracellular. Of the extracellular water, three-quarters is interstitial fluid, and one-quarter is intravascular fluid. One blood component is blood sugar, which refers to a concentration of glucose in blood. The concentration of glucose contained in the blood flowing along a capillary vessel is similar to that of the interstitial fluid.
Human body tissue consists of flexible cells with interstitial fluid therebetween. When an external pressure is applied to tissue of a human body, the tissue is depressed and the interstitial fluid moves within the body.
When a spectrum of a blood component is measured, the measured result may vary in accordance with a variety of conditions such as a surface state of a measured tissue, a pressure applied to the tissue, and other similar conditions. Therefore, in order to predict a concentration of a specific component in the tissue, there is a need for active control of the measured tissue. Accordingly, how the tissue measured is controlled is methodologically important.
FIG. 1 is a graph illustrating absorption spectra of major blood components. FIG. 2 is a graph illustrating absorbance variations of a web tissue having a thickness of 1.7 mm. FIGS. 1 and 2 illustrate the importance of an active control and control method.
FIG. 1 includes absorbance spectra of major blood components such as glucose, hemoglobin, albumin, triacetine, and gamma (γ)-globulin and an absorbance spectrum of water. The absorbance spectra of hemoglobin G2, glucose G3, albumin G4, triacetine G5, and gamma (γ)-globulin G6 are obtained by extracting the absorbance spectrum of the water G1 from an absorbance spectrum (not shown) of an aqueous solution of each component having a path length of 0.5 mm with respect to light having a wavelength in the near infrared range.
In FIG. 1, the left-longitudinal axis represents an absorbance of each of the major blood components and the right-longitudinal axis represents an absorbance of the water.
As shown in FIG. 1, the absorbance of the water at each of the wavelengths 1600 nm and 2200 nm is more than twenty times greater than those of the other blood components. It can be further noted that the near infrared light absorption band of the glucose and the near infrared light absorption bands of the other blood components overlap one another.
As optical technologies and statistical analysis technologies improve, research is being conducted into non-invasively measuring blood sugar using light in the near infrared range. Thus far, however, satisfactory results have not been achieved due to a variety of causes such as light scattering, a relatively high absorbance of water, an interference caused by the overlap of the near infrared light absorption bands of the glucose and other blood components, and a diversity of the tissue to be examined.
Accordingly, when the blood components are measured using light in the near infrared range, the tissue to be examined should be properly controlled in a direction in which a signal-to-noise ratio is increased by enlarging a variation of the body fluid while correcting an influence of the tissue that may vary each time the measurement is performed, considering the results shown in FIG. 1.
Experimentally, an absorbance of an aqueous solution having a thickness of 0.5 mm and containing 500 mg of glucose was measured using a conventional apparatus and method. The absorbance of the glucose may be isolated, and thereby obtained, by extracting the absorbance of the water from the whole absorbance of the aqueous solution.
The measured results are shown in Table 1. The measured results shown in Table 1 correspond to the absorbance of the glucose contained in a soft tissue having a thickness of 2 mm.
TABLE 1Wavelength16892094223822742360(nm)(peak)(peak)(valley)(peak)(peak)Absorbance0.00060.00460.002090.002460.00507
An absorbance variation of a 1.7 mm thickness web tissue between a thumb and an index finger was further measured using the conventional apparatus and method. FIG. 2 shows the results of this measurement.
Through the measured results shown in FIG. 2, the absorbance variation of the web tissue having a thickness greater than 1.7 mm can be assumed.
Referring to FIG. 2, it can be noted that, when light having a wavelength of 1650 nm is used, the absorbance variation is about ±0.03 Abs. It can be further noted that, when light having a wavelength of 2200 nm is used, the absorbance variation is about ±0.05 Abs.
When comparing results shown in Table 1 with the results of FIG. 2, it can be noted that, when light having a wavelength of 1650 nm is used, the repeated measuring error (±0.03 Abs) is 50 times greater than the absorbance (0.0006 Abs) of the glucose. It can be further noted that, when light having a wavelength of 2200 nm is used, the repeated measuring error (0.05 Abs) is about 24 times greater than the absorbance (0.00209 Abs).
As described above, when blood components such as blood sugar are measured without properly controlling the tissue being measured, an absorbance variation according to the repeated measurements becomes much greater than the actual absorbance of the tissue to be examined. When the absorbance variation increases, the reproducibility deteriorates. That is, the absorbance of a tissue measured may vary at every measurement. As a result, the absorbance measuring results are not reliable and the blood component data obtained through the absorbance analysis are indefensible.